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    <title>Using canvas with d3.js, an introduction</title>
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        <h1>Using canvas with d3.js, an introduction</h1>
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        <br />
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        <br /><br />
        <p style="max-width: 700px; margin: auto">
          <code>canvas</code> is an HTML element which can be used to draw
          graphics. It is an alternative to <code>svg</code>
        </p>
      </div>
    </header>

    <!-- TABLE of CONTENT -->
    <div>
      <nav class="col-sm-3 col-4" id="myScrollspy">
        <ul class="nav nav-pills flex-column">
          <li class="nav-item">
            <a class="nav-link active" href="#basic">Most basic shape</a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#rectangle">Rectangle</a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#publication">Publication</a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#dark">Dark mode</a>
          </li>
        </ul>
      </nav>
    </div>

    <!-- ==================== Most Basic shape ==================== -->

    <section id="basic" class="bg">
      <div class="container">
        <h1>Just one shape</h1>
        <hr />
        <div class="row">
          <!-- ==================== GRAPH SECTION = WHERE THE GRAPH APPEARS ==================== -->
          <div class="col-lg-6 .align-middle">
            <div style="position: -webkit-sticky; position: sticky; top: 120px">
              <div class="bg" id="res-sectionA"></div>
              <br />
              <div>
                <h5>Notes:</h5>
                <ul>
                  <br />
                  <li>
                    Start by creating a <code>canvas</code> element in the html.
                    Give it an id. It creates a fixed-size drawing surface that
                    exposes one or more rendering contexts
                  </li>
                  <br />
                  <li></li>
                  <br />
                  <li></li>
                  <br />
                  <li>
                    <u>Note</u>: rectangle is the only primitive shape offered
                    in canvas. All other shapes must be created using one or
                    more paths.
                  </li>
                </ul>
              </div>
            </div>
          </div>

          <!-- ==================== CODE SECTION = WHERE THE CODE APPEARS ==================== -->
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            <!-- ========= show html code ============== -->
            <aside
              style="position: -webkit-sticky; position: sticky; top: 120px"
            >
              &larr; Edit me!
            </aside>
            <pre
              class="language-html"
            ><code id="html-sectionA" contenteditable="true"><xmp><!DOCTYPE html>
<meta charset="utf-8">

<!-- Create a div where the graph will take place -->
<canvas id="my_dataviz" width="400" height="400">
</canvas>


</xmp></code></pre>
            <!-- ==================================== -->

            <!-- ========= show JS code ==============  -->
            <pre
              class="language-js"
            ><code id="js-sectionA" contenteditable="true"><xmp><script>

// select the canvas element created in the html
var canvas = document.getElementById('my_dataviz');

// Get the 'context'
var ctx = canvas.getContext('2d');

// Build a rectangle
ctx.fillStyle = '#69b3a2'; // rectangle color
ctx.fillRect(20, 20, 50, 50); // 4 arguments for the rect features: x, y, width and height

</script></xmp></code></pre>
            <!-- ==================================== -->

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            <script>
              // At the beginning, I read the html and JS fragments
              myHtmlParser("html-sectionA", "res-sectionA");
              myJSParser("js-sectionA", "res-sectionA");

              // If the user change the JS fragment, I run it again:
              document
                .getElementById("js-sectionA")
                .addEventListener("input", function () {
                  d3.select("#res-sectionA").html("");
                  myHtmlParser("html-sectionA", "res-sectionA");
                  myJSParser("js-sectionA", "res-sectionA");
                });

              // If the user change the HTML fragment, I run it again:
              document
                .getElementById("html-sectionA")
                .addEventListener("input", function () {
                  d3.select("#res-sectionA").html("");
                  myHtmlParser("html-sectionA", "res-sectionA");
                  myJSParser("js-sectionA", "res-sectionA");
                });
            </script>
          </div>
        </div>
      </div>
    </section>
    <br />

    <!-- ==================== Rectangles ==================== -->

    <section id="rectangle" class="bg">
      <div class="container">
        <h1>Drawing rectangles</h1>
        <hr />
        <div class="row">
          <!-- ==================== GRAPH SECTION = WHERE THE GRAPH APPEARS ==================== -->
          <div class="col-lg-6 .align-middle">
            <div style="position: -webkit-sticky; position: sticky; top: 120px">
              <div class="bg" id="res-sectionB"></div>
              <br />
              <div>
                <h5>Rectangles are drawn using 3 functions:</h5>
                <ul>
                  <br />
                  <li>
                    <code>fillRect</code>: to create a filled rectangle. 4
                    arguments: <code>x</code>, <code>y</code>,
                    <code>width</code> and <code>height</code>.
                  </li>
                  <br />
                  <li><code>strokeRect</code>: to draw just the outline</li>
                  <br />
                  <li>
                    <code>clearRect</code>: to clear all the pixel under this
                    rectangle
                  </li>
                </ul>
              </div>
            </div>
          </div>

          <!-- ==================== CODE SECTION = WHERE THE CODE APPEARS ==================== -->
          <div class="col-lg-6 text-center .align-middle">
            <!-- ========= show html code ============== -->
            <aside
              style="position: -webkit-sticky; position: sticky; top: 120px"
            >
              &larr; Edit me!
            </aside>
            <pre
              class="language-html"
            ><code id="html-sectionB" contenteditable="true"><xmp><!DOCTYPE html>
<meta charset="utf-8">

<!-- Create a div where the graph will take place -->
<canvas id="my_dataviz2" width="400" height="400">
</canvas>

</xmp></code></pre>
            <!-- ==================================== -->

            <!-- ========= show JS code ==============  -->
            <pre
              class="language-js"
            ><code id="js-sectionB" contenteditable="true"><xmp><script>

// select the canvas element created in the html
var canvas = document.getElementById('my_dataviz2');

// Get the 'context'
var ctx = canvas.getContext('2d');

// Left: filled rectangle
ctx.fillStyle = '#69b3a2'; // rectangle color
ctx.fillRect(10, 10, 50, 50); // 4 arguments for the rect features: x, y, width and height

// Center: rectangle outline
ctx.strokeRect(100, 100, 80, 80);

// Right: rectangle with a cleared area
ctx.fillRect(200, 200, 120, 120);
ctx.clearRect(210, 170, 80, 80);

</script></xmp></code></pre>
            <!-- ==================================== -->

            <!-- ==================== JAVASCRIPT SECTION : EXECUTE THIS CODE AND MAKE IT INTERACTIVE ==================== -->
            <script>
              // At the beginning, I read the html and JS fragments
              myHtmlParser("html-sectionB", "res-sectionB");
              myJSParser("js-sectionB", "res-sectionB");

              // If the user change the JS fragment, I run it again:
              document
                .getElementById("js-sectionB")
                .addEventListener("input", function () {
                  d3.select("#res-sectionB").html("");
                  myHtmlParser("html-sectionB", "res-sectionB");
                  myJSParser("js-sectionB", "res-sectionB");
                });

              // If the user change the HTML fragment, I run it again:
              document
                .getElementById("html-sectionB")
                .addEventListener("input", function () {
                  d3.select("#res-sectionB").html("");
                  myHtmlParser("html-sectionB", "res-sectionB");
                  myJSParser("js-sectionB", "res-sectionB");
                });
            </script>
          </div>
        </div>
      </div>
    </section>
    <br />

    <!-- ==================== Most basic path: TRIANGLE ==================== -->

    <section id="publication" class="bg">
      <div class="container">
        <h1>Most basic path: triangle</h1>
        <hr />
        <div class="row">
          <!-- ==================== GRAPH SECTION = WHERE THE GRAPH APPEARS ==================== -->
          <div class="col-lg-6 .align-middle">
            <div style="position: -webkit-sticky; position: sticky; top: 120px">
              <div class="bg" id="res-sectionC"></div>
              <br />
              <div>
                <h5>
                  Path is the second and <u>last</u> primitive you can use.
                  Steps:
                </h5>
                <ul>
                  <br />
                  <li>Initialize with <code>beginPath()</code>.</li>
                  <br />
                  <li>
                    Set the coordinate you want to start from with
                    <code>moveTo()</code>.
                  </li>
                  <br />
                  <li>
                    Use <code>lineTo()</code> to build as many segments as you
                    need.
                  </li>
                  <br />
                  <li>
                    Fill the shape with <code>fill()</code>, and/or draw the
                    stroke with <code>stroke</code>
                  </li>
                </ul>
              </div>
            </div>
          </div>

          <!-- ==================== CODE SECTION = WHERE THE CODE APPEARS ==================== -->
          <div class="col-lg-6 text-center .align-middle">
            <!-- ========= show html code ============== -->
            <aside
              style="position: -webkit-sticky; position: sticky; top: 120px"
            >
              &larr; Edit me!
            </aside>
            <pre
              class="language-html"
            ><code id="html-sectionC" contenteditable="true"><xmp><!DOCTYPE html>
<meta charset="utf-8">

<!-- Create a div where the graph will take place -->
<canvas id="my_dataviz3" width="400" height="400">
</canvas>

</xmp></code></pre>
            <!-- ==================================== -->

            <!-- ========= show JS code ==============  -->
            <pre
              class="language-js"
            ><code id="js-sectionC" contenteditable="true"><xmp><script>

// select the canvas element created in the html
var canvas = document.getElementById('my_dataviz3');

// Get the 'context'
var ctx = canvas.getContext('2d');

// Set the color:
ctx.fillStyle = '#D8D8D8';

// Initialize path
ctx.beginPath();

// Go to the starting coordinate
ctx.moveTo(100, 50);

// Draw 2 segments
ctx.lineTo(300, 50);
ctx.lineTo(200, 370);

// Fill the shape
ctx.fill();
ctx.stroke();

</script></xmp></code></pre>
            <!-- ==================================== -->

            <!-- ==================== JAVASCRIPT SECTION : EXECUTE THIS CODE AND MAKE IT INTERACTIVE ==================== -->
            <script>
              // At the beginning, I read the html and JS fragments
              myHtmlParser("html-sectionC", "res-sectionC");
              myJSParser("js-sectionC", "res-sectionC");

              // If the user change the JS fragment, I run it again:
              document
                .getElementById("js-sectionC")
                .addEventListener("input", function () {
                  d3.select("#res-sectionC").html("");
                  myHtmlParser("html-sectionC", "res-sectionC");
                  myJSParser("js-sectionC", "res-sectionC");
                });

              // If the user change the HTML fragment, I run it again:
              document
                .getElementById("html-sectionC")
                .addEventListener("input", function () {
                  d3.select("#res-sectionC").html("");
                  myHtmlParser("html-sectionC", "res-sectionC");
                  myJSParser("js-sectionC", "res-sectionC");
                });
            </script>
          </div>
        </div>
      </div>
    </section>
    <br />

    <!-- ==================== CIRCLE==================== -->

    <section id="circle" class="bg">
      <div class="container">
        <h1>Circle</h1>
        <hr />
        <div class="row">
          <!-- ==================== GRAPH SECTION = WHERE THE GRAPH APPEARS ==================== -->
          <div class="col-lg-6 .align-middle">
            <div style="position: -webkit-sticky; position: sticky; top: 120px">
              <div class="bg" id="res-sectionD"></div>
              <br />
              <div>
                <h5>Notes:</h5>
                <ul>
                  <br />
                  <li>
                    A circle is a path, made using the
                    <code>arc()</code> function.
                  </li>
                  <br />
                  <li>
                    You have to provide <code>x</code>, <code>y</code>,
                    <code>radius</code>, <code>startAngle</code> and
                    <code>endAngle</code>.
                  </li>
                </ul>
              </div>
            </div>
          </div>

          <!-- ==================== CODE SECTION = WHERE THE CODE APPEARS ==================== -->
          <div class="col-lg-6 text-center .align-middle">
            <!-- ========= show html code ============== -->
            <aside
              style="position: -webkit-sticky; position: sticky; top: 120px"
            >
              &larr; Edit me!
            </aside>
            <pre
              class="language-html"
            ><code id="html-sectionD" contenteditable="true"><xmp><!DOCTYPE html>
<meta charset="utf-8">

<!-- Create a div where the graph will take place -->
<canvas id="my_dataviz4" width="400" height="400">
</canvas>

</xmp></code></pre>
            <!-- ==================================== -->

            <!-- ========= show JS code ==============  -->
            <pre
              class="language-js"
            ><code id="js-sectionD" contenteditable="true"><xmp><script>

// select the canvas element created in the html
var canvas = document.getElementById('my_dataviz4');

// Get the 'context'
var ctx = canvas.getContext('2d');

// Set the color:
ctx.fillStyle = '#D8D8D8';

// Initialize path
ctx.beginPath();

// Build a circle
ctx.arc(200, 200, 100, 0, Math.PI * 2)

// Show the stroke
ctx.stroke()

</script></xmp></code></pre>
            <!-- ==================================== -->

            <!-- ==================== JAVASCRIPT SECTION : EXECUTE THIS CODE AND MAKE IT INTERACTIVE ==================== -->
            <script>
              // At the beginning, I read the html and JS fragments
              myHtmlParser("html-sectionD", "res-sectionD");
              myJSParser("js-sectionD", "res-sectionD");

              // If the user change the JS fragment, I run it again:
              document
                .getElementById("js-sectionD")
                .addEventListener("input", function () {
                  d3.select("#res-sectionD").html("");
                  myHtmlParser("html-sectionD", "res-sectionD");
                  myJSParser("js-sectionD", "res-sectionD");
                });

              // If the user change the HTML fragment, I run it again:
              document
                .getElementById("html-sectionD")
                .addEventListener("input", function () {
                  d3.select("#res-sectionD").html("");
                  myHtmlParser("html-sectionD", "res-sectionD");
                  myJSParser("js-sectionD", "res-sectionD");
                });
            </script>
          </div>
        </div>
      </div>
    </section>
    <br />

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      style="padding-top: 70px; padding-bottom: 70px"
    >
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                  <li>
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